One of the known constructions to obtain the fixation of the rotor of an electric motor to the crankshaft of the compressor uses mounting by mechanical interference. In this prior art arrangement, the rotor is heated to a certain temperature, which is insufficient to damage its structure, but which promotes a thermal dilatation that is necessary to allow the introduction of the crankshaft inside the rotor, without requiring mechanical efforts that may impair the structure of the rotor. After introducing the crankshaft into the rotor, the latter, already under a cooling process, exerts pressure around the crankshaft by thermal contraction, guaranteeing the rotational and axial locking between the rotor and the crankshaft.
In this type of rotor-crankshaft assembly, the heating of the rotor is effected at a temperature that is high enough to promote thermal dilatation, which will minimize the axial efforts to be imparted to the rotor during its mounting to the crankshaft, being also considered that the difference between the nominal diameters of the crankshaft and of the rotor should have such a value as to guarantee the necessary interference upon completion of the mounting operation.
In the most widely used rotors, such as for example those in which the magnets are mounted between a rotor core and a steel cover, the structure of the rotor is strong enough to support heating and the axial efforts which are necessary to promote the fitting of the crankshaft into the rotor. These rotors of a well known construction, for instance with a steel cover surrounding the magnets, have a structure that is strong enough to allow a simple and cost effective mounting of the rotor to the crankshaft, by mechanical interference with previous heating.
However, in other rotors, such as for example, those in which the magnets are affixed to the rotor core only by gluing, dispensing the use of the external steel cover, the resulting structure, although being simpler, less expensive, and electromagnetically more efficient, is not strong enough to withstand, with no risks of damages, the efforts and the temperature to which it is submitted if mounted by interference with previous heating. The heating to be applied to the rotor, so that it may be mounted around the crankshaft, jeopardizes the gluing of the magnets around the rotor core or other structural characteristics, impairing the reliability of the compressor to be produced.
The mounting solutions by interference without heating, although being acceptable in certain situations in which the rotors are structurally more resistant, are achieved by applying, to the rotor and to the external end of the crankshaft, opposite axial forces which, during the mounting operation, are easily misaligned by positioning deviations of the retaining means and the driving means which are applied to both the crankshaft and the rotor. This possibility of misalignment is mainly due to the fact that the axial force applied to the crankshaft is compressive, acting against the end of the crankshaft opposite to the rotor. The mounting misalignments, even being small, tend to provoke unacceptable deformations in the assembly to be formed.
The mounting solutions, which have been proposed to such rotors of fragile construction, require complex procedures that will increase the cost of the final product, as it occurs, for example, when the fixation of the rotor to the crankshaft is made by gluing.